Prediction of feasibility of a chemical reaction

Prediction of Feasibility of a Chemical Reaction

Predicting whether a chemical reaction will occur spontaneously under given conditions is a fundamental part of chemistry. This is especially important in electrochemistry, where redox reactions are governed by electrode potentials and energy changes. The feasibility of a reaction can be determined using thermodynamic concepts and electrochemical data such as electrode potentials and Gibbs free energy.

Electrode Potential and Feasibility

In electrochemistry, the feasibility of a redox reaction is often predicted by calculating the cell potential (EMF) of the electrochemical cell:

EMF (E_cell) = E_cathode - E_anode

• A positive value of E_cell (E_cell > 0) indicates that the reaction can proceed spontaneously under standard conditions.
• A negative value of E_cell (E_cell < 0) suggests that the reaction is not spontaneous and will not take place on its own.

Connection Between Gibbs Free Energy and Cell Potential

The change in Gibbs free energy (ΔG) is a key factor in assessing the spontaneity of a reaction. Its relationship with the cell potential (EMF) is given by the following equation:

ΔG = –nFE_cell

Where:

• ΔG is the change in Gibbs free energy (in joules)
• n is the number of electrons transferred
• F is the Faraday constant (96,500 C/mol)
• E_cell is the cell potential (in volts)

• When ΔG < 0, the chemical reaction is thermodynamically favorable.
• If ΔG > 0: The reaction is not feasible (non-spontaneous).

Using the Electrochemical Series

The electrochemical series is a table of standard reduction potentials. It helps determine which species will act as the oxidizing or reducing agent in a reaction. A species with a higher reduction potential tends to get reduced, while one with a lower reduction potential gets oxidized.

Example

Consider the redox reaction:

Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)

Standard electrode potentials:

• E°(Cu²⁺/Cu) = +0.34 V
• E°(Zn²⁺/Zn) = –0.76 V

So, E_cell = 0.34 – (–0.76) = +1.10 V → Feasible reaction

The feasibility of a chemical reaction can be accurately predicted using cell potentials and Gibbs free energy. If a reaction has a positive EMF and a negative ΔG, it is considered spontaneous and thermodynamically favorable.